With recently increasing use of automobiles as public transportation, there have occurred several social problems. Among them are air pollution and the consumption of fossil fuels, especially petroleum.
Some measures have been taken to reduce harmful substances in exhaust gas, but this also caused the degradation of the overall efficiency of the internal combustion engine (hereafter referred simply to as engine). For the purpose of preventing the degradation of the operating efficiency of engine and improving the measures against exhaust gas, an electronic control apparatus has come to be employed which has improved control precision. For example, there have been proposed an electronically controlled fuel injection apparatus and an electronically controlled ignition timing apparatus, and most recently an ignition apparatus controlled by a microprocessor.
The conventional trend in such a control apparatus is toward the mere replacement of mechanical control by an electric one and therefore the individual controlled objects must be provided with the associated electronic control units.
The control of an engine should suppress the harmful components in exhaust gases and operate the engine with a high efficiency. The assembly of the separate electronic control units provided for the controlled objects, e.g. the electronically controlled fuel injection apparatus and the electronically controlled ignition timing apparatus, as described above, has a poor interrelation among the control units so that a close control of the overall control system is impossible. Moreover, such a composite control system must be accompanied by extremely complicated circuits.